I hope this 'first timer' post does not sound too stupid.
I have been reading the following threads with interest (along with countless other threads):
http://www.ageod-forum.com/showthread.php?t=11732
http://www.ageod-forum.com/showthread.php?p=69220#post69220
I feel comfortable with the concepts of merging together small units with available (empty) element slots. However, I have having some trouble trying to merge fleet units.
The second thread noted above suggests that blockade fleets can allow for 2 heavy warships and 8 light warships. The at start forces for the Union include a number of fleets that consist of 2 heavy warships and 6 light warships. I cannot seem to fill the suposed 2 extra 'light' spaces. I do not see a 'merge' option/button for fleets/ships (whether or not the combination is available/allowable). In addition, the second thread also suggests that transport fleets can consist of 4 transport elements. Again, the at start forces for the union contain a number of transport fleets containing 2 ships/elements used, i.e. 2 empty slots, but I cannot seem to merge two together.
I suspect that the answer to this problem is either:
1) you simply can't do it at all.
2) I have missed somthing really obvious

Alternatively, is there any need to merge fleet units? as having the desired ships / elements within a stack, whetrher merged together or not, has the same end result / effectiveness anyway?
Please put me out of my misery.
Just in case it made a difference... I have waited until the relevant units have become 'unlocked' after the initial start of the campaign.
Regards